Practice Free 305-300 LPIC-3: Virtualization and Containerization - Exam 305, version 3.0 Exam Questions Answers With Explanation

The command virsh pool-create-as vms dir --target /vms creates and starts a transient storage pool named vms of type dir with the target directory /vms12. This command resolves the issue of the storage pool not found error, as it makes the existing directory /vms visible to libvirt as a storage pool. The other commands are invalid because:

dd if=/dev/zero of=/vms bs=1 count=0 flags=name:vms is not a valid command syntax. The dd command does not take a flags argument, and the output file /vms should be a regular file, not a directory3.

libvirt-poolctl new --name=/vms --type=dir --path=/vms is not a valid command name. There is no such command as libvirt-poolctl in the libvirt package4.

qemu-img pool vms:/vms is not a valid command syntax. The qemu-img command does not have a pool subcommand, and the vms:/vms argument is not a valid image specification5.

touch /vms/.libvirtpool is not a valid command to create a storage pool. The touch command only creates an empty file, and the .libvirtpool file is not recognized by libvirt as a storage pool configuration file6.

References:

1: virsh - difference between pool-define-as and pool-create-as - Stack Overflow

2: dd(1) - Linux manual page - man7.org

3: 12.3.3. Creating a Directory-based Storage Pool with virsh - Red Hat Customer Portal

4: libvirt - Linux Man Pages (3)

5: qemu-img(1) - Linux manual page - man7.org

6: touch(1) - Linux manual page - man7.org

 cloud-init uses the /var/lib/cloud/ directory to store status information and configuration information retrieved from external sources, such as the cloud platform’smetadata service or user data files. The directory contains subdirectories for different types of data, such as instance, data, handlers, scripts, and sem. The instance subdirectory contains information specific to the current instance, such as the instance ID, the user data, and the cloud-init configuration. The data subdirectory contains information about the data sources that cloud-init detected and used. The handlers subdirectory contains information about the handlers that cloud-init executed. The scripts subdirectory contains scripts that cloud-init runs at different stages of the boot process, such as per-instance, per-boot, per-once, and vendor. The sem subdirectory contains semaphore files that cloud-init uses to track the execution status of different modules and stages. References:

Configuring and managing cloud-init for RHEL 8 - Red Hat Customer Portal

vsphere - what is the linux file location where the cloud-init user …

The FROM statement in a Dockerfile specifies the base image from which the subsequent instructions are executed1. The value of the FROM statement can be either an image name, an image name with a tag, or an image ID1. The image name can be either a repository name or a repository name with a registry prefix2. For example, ubuntu is a repository name, and docker.io/ubuntu is a repository name with a registry prefix2. The tag is an optional identifier that can be used to specify a particular version or variant of an image1. For example, ubuntu:focal refers to the image with the focal tag in the ubuntu repository2. The image ID is a unique identifier that is automatically generated when an image is built or pulled1. For example, sha256:9b0dafaadb1cd1d14e4db51bd0f4c0d56b6b551b2982b2b7c637ca143ad605d2 is an image ID3.

Therefore, the only valid value in the FROM statement among the given options is ubuntu:focal, which is an image name with a tag. The other options are invalid because:

docker://ubuntu:focal is not a valid image name format. The docker:// prefix is used to specify a transport protocol, not a registry prefix4.

registry:ubuntu:focal is not a valid image name format. The registry prefix should be a valid hostname or IP address, not a generic term2.

file:/tmp/ubuntu/Dockerfile is not a valid image name format. The file: prefix is used to specify a local file path, not an image name5.

http://docker.example.com/images/ubuntu-focal.iso is not a valid image name format.  The http:// prefix is used to specify a web URL, not an image name 5.

References:

1: Dockerfile reference | Docker Docs

2: docker - Using FROM statement in dockerfile - Stack Overflow

3: How to get the image id from a docker image - Stack Overflow

4: skopeo - Docker Registry v2 API tool - Linux Man Pages (1)

5: How to build a Docker image from a local Dockerfile? - Stack Overflow

The file procs in a cgroup directory contains the list of processes belonging to this cgroup. Each line in the file shows the PID of a process that is a member of the cgroup. A process can be moved to a cgroup by writing its PID into the cgroup’s procs file. For example, to move the process with PID 24982 to the cgroup cg1, the following command can be used: echo 24982 > /sys/fs/cgroup/cg1/procs1. The file procs is different from the file tasks, which lists the threads belonging to the cgroup. The file procs can be used to move all threads in a thread group at once, while the file tasks can be used to move individual threads2. References:

Creating and organizing cgroups · cgroup2 - GitHub Pages

Control Groups — The Linux Kernel documentation

The type attribute of a element in a libvirt domain definition specifies the hypervisor used for running the domain. The allowed values are driver specific, but include “xen”, “kvm”, “hvf” (since 8.1.0 and QEMU 2.12), “qemu” and "lxc"1. Therefore, the valid values among the options are C. kvm and E. lxc. KVM stands for Kernel-based Virtual Machine, which is a full virtualization solution for Linux on x86 hardware containing virtualization extensions (Intel VT or AMD-V)2. LXC stands for Linux Containers, which is an operating system-level virtualization method for running multiple isolated Linux systems (containers) on a single control host3. The other options are not valid values for the type attribute, asthey are either not hypervisors or not supported by libvirt. References:http://libvirt.org/formatdomain.html

https://libvirt.org/formatcaps.html

The firmware attribute of the element in a libvirt domain definition specifies the type of firmware used to boot the virtual machine. The valid values for this attribute are efi and bios, which correspond to the Extensible Firmware Interface (EFI) and the Basic Input/Output System (BIOS) respectively. EFI is a newer standard that supports more features and security than BIOS, such as Secure Boot and faster boot times. BIOS is an older standard that is widely compatible and supported by most hypervisors and operating systems. The other values, scsi, virtio, and pcie, are not related to firmware, but to different types of devices or drivers that can be used in a virtual machine. References: 1 (search for firmware enum)

 Container-based virtualization is a method of operating system-level virtualization that allows multiple isolated user spaces (containers) to run on the same host system1. Each container shares the same operating system kernel as the host, but has its own file system, libraries, and processes2. Therefore, the statements A and C are false, as containers do not run their own kernels or rely on hardware support from the CPU. The statement E is also false, as Linux does support container-based virtualization through various technologies, such as cgroups, namespaces, LXC, Docker, etc12. The statement B is true, as different containers may use different distributions of the same operating system, such as Debian, Ubuntu, Fedora, etc., as long as they are compatible with the host kernel3. The statement D is also true, as all containers run within the operating system kernel of the host system, which provides isolation and resource management for them12. References:

1: Containerization (computing) - Wikipedia.

2: What are containers? | Google Cloud.

3: What is Container-Based Virtualization? - StackHowTo.

The purpose of the packer inspect subcommand is to display an overview of the configuration contained in a Packer template1. A Packer template is a file that defines the various components a Packer build requires, such as variables, sources, provisioners, and post-processors2. The packer inspect subcommand can help you quickly learn about a template without having to dive into the HCL (HashiCorp Configuration Language) itself1. The subcommand will tell you things like what variables a template accepts, the sources it defines, the provisioners it defines and the order they’ll run, and more1.

The other options are not correct because:

A) Retrieve files from an existing Packer image. This is not the purpose of the packer inspect subcommand. To retrieve files from an existing Packer image, you need to use the packer scp subcommand, which copies files from a running instance of a Packer image to your local machine2.

B) Execute commands within a running instance of a Packer image. This is not the purpose of the packer inspect subcommand. To execute commands within a running instance of a Packer image, you need to use the packer ssh subcommand, which connects to a running instance of a Packer image via SSH and runs the specified command2.

C) List the artifacts created during the build process of a Packer image. This is not the purpose of the packer inspect subcommand. To list the artifacts created during the build process of a Packer image, you need to use the packer build subcommand with the -machine-readable flag, which outputs the build information in a machine-friendly format that includes the artifact details2.

D) Show usage statistics of a Packer image. This is not the purpose of the packer inspect subcommand. To show usage statistics of a Packer image, you need to use the packer console subcommand with the -stat flag, which launches an interactive console that allows you to inspect and modify variables, sources, and functions, and displays the usage statistics of the current session2. References: 1: packer inspect - Commands | Packer | HashiCorp Developer 2: Commands | Packer | HashiCorp Developer

Libvirt supports creating and managing various types of virtual networks that can be used to connect virtual machines to each other or to the external network. One of the common types of virtual networks is the NAT-based network, which uses network address translation (NAT) to allow virtual machines to access the outside world through the host’s network interface. By default, libvirt creates a NAT-based network called ‘default’ when it is installed and started. This network appears as a standard Linux bridge device on the host system, named virbr0. The bridge device has an IP address of 192.168.122.1/24 and acts as a gateway and a DHCP server for the virtual machines connected to it. The bridge device also has iptables rules to forward and masquerade the traffic from and to the virtual machines. The virtual machines connected to the ‘default’ network have their own IP addresses in the 192.168.122.0/24 range and their own MAC addresses generated by libvirt. The virtual machines can communicate with each other, with the host, and with the external network through the bridge device and the NAT mechanism12.

The other statements in the question are false regarding networking with libvirt. Libvirt’s network functionality is not limited to connecting virtual machines to a physical network interface of the host system. Libvirt can also create isolated networks that do not have any connection to the outside world, or routed networks that use static routes to connect virtual machines to the external network without NAT3. Libvirt does not assign the same MAC address to all virtual machines and isolate their network interfaces at the link layer. Libvirt assigns a unique MAC address to each virtual machine and allows them to communicate with each other at the network layer4. Libvirt does not require a dedicated network interface that may not be used by the host system. Libvirt can share the host’s network interface with the virtual machines using NAT or bridging, or it can pass a physical network interface to a virtual machine exclusively using PCI passthrough5. Libvirt does not support exactly one virtual network and connect all virtual machines to it. Libvirt supports creating and managing multiple virtual networks with different names and configurations, and connecting virtual machines to different networks according to their needs6. References:

libvirt: Virtual Networking

libvirt: NAT forwarding (aka “virtual networks”)

libvirt: Routed network

libvirt: MAC address

libvirt: PCI passthrough of host network devices

[libvirt: Network XML format]

LXC implements system containers, which are a type of operating-system-level virtualization. System containers allow running multiple isolated Linux systems on a single Linux control host, using a single Linux kernel. System containers share the same kernel with the host and each other, but have their own file system, libraries, andprocesses. System containers are different from application containers, which are designed to run a single application or service in an isolated environment. Application containers are usually smaller and more portable than system containers, but also more dependent on the host kernel and libraries. Hardware containers, CPU emulation, and paravirtualization are not related to LXC, as they are different kinds of virtualization methods that involve hardware abstraction, instruction translation, or modification of the guest operating system. References:

1: LXC - Wikipedia

2: Linux Virtualization : Linux Containers (lxc) - GeeksforGeeks

3: Features - Proxmox Virtual Environment

IaaS is a type of cloud computing service that offers essential compute, storage, and networking resources on demand, on a pay-as-you-go basis. IaaS is one of the four types of cloud services, along with software as a service (SaaS), platform as a service (PaaS), and serverless12. IaaS eliminates the need for enterprises to procure, configure, or manage infrastructure themselves, and they only pay for what they use23. Some examples of IaaS providers are Microsoft Azure, Google Cloud, and Amazon Web Services.

 LXD supports the following network interface types for containers: macvlan, bridged, physical, sriov, and ovn1. Macvlan creates a virtual interface on the host that is connected to the same network as the parent interface2. Bridged connects the container to a network bridge that acts as a virtual switch3. Physical attaches the container to a physical network interface on the host2. Ipsec and wifi are not valid network interface types for LXD containers. References:

1: Bridge network - Canonical LXD documentation

2: How to create a network - Canonical LXD documentation

4: LXD containers and networking with static IP - Super User

LXD supports the following network interface types in an LXD container configuration1:

macvlan: Creates a virtual interface on the host with a unique MAC address and attaches it to an existing physical interface. This allows the container to have direct access to the physical network, but prevents communication with the host and other containers on the same host2.

bridged: Connects the container to an existing bridge interface on the host. This allows the container to communicate with the host and other containers on the same bridge, as well as the external network if the bridge is connected to a physical interface3.

physical: Passes an existing physical interface on the host to the container. This allows the container to have exclusive access to the physical network, but removes the interface from the host4.

The other network interface types, ipsec and wifi, are not valid in an LXD container configuration. Ipsec is a protocol for secure communication over IP networks, not a network interface type. Wifi is a wireless technology for connecting devices to a network, not a network interface type. References:

About networking - Canonical LXD documentation

Macvlan network - Canonical LXD documentation

Bridge network - Canonical LXD documentation

Physical network - Canonical LXD documentation